1. Field of the Invention
The present invention relates to a method for restricting access to sensitive contents of digital images alongside a system for the implementation of the method. The restriction is commonly applied to human faces, vehicle registration plates and content intended for adult recipients only.
The system for restricting access to sensitive contents of digital images according to the invention contains the encoding and decoding unit. In the encoding unit, the acquisition module is connected through the automatic sensitive area detection module with the sensitive contents encoding module and further with the compression module. A memory buffer is added to the automatic detection of sensitive patterns module. In the decoding unit, the stream decoding module is connected directly with the module for decoding the sensitive image contents.
2. Description of the Related Art
Further works in the same area facilitated the improvement of the selected system parameters at the expense of the remaining ones. So far it has not been possible to develop a method which would allow for high quality restoration for lossy JPEG compression at the level of 70-80, used in practice.
In the article “Images with Self-correcting Capabilities” by J. Fridrich and M. Goljan presented on the IEEE International Conference on Image Processing it was shown for the first time that it is possible to encode digital images in such a way that it is feasible to restore the fragments modified in any manner to a simplified version of the original contents. The simplification mentioned here consisted in encoding in the picture its lossy-compressed version stemming from the use of low-quality MEG representation. Despite the low reconstruction fidelity, a human would typically be able to recognize the restored content. Additionally, an image protected in this way needs to be stored in its lossless format as the lossy compression results in corruption of the additionally hidden information. The authors managed to gain robustness against JPEG compression with the quality level above 90 at the expense of significant loss of quality. In such conditions the expected image quality, expressed in terms of a peak-signal-to-noise-ratio, drops to 33 dB and 21 dB for the complete image and the restored fragments, respectively.